Solid propellant composition containing gelled hydrazine

ABSTRACT

1. A method for the preparation of a propellant composition which comprises the steps of A. STIRRING ANTIMONYL POTASSIUM TARTRATE CRYSTALS INTO A SOLUTION CONSISTING OF HYDRAZINE AND SODIUM CARBOXYMETHYLCELLULOSE AT ROOM TEMPERATURE UNTIL A HOMOGENEOUS MIXTURE RESULTS, AND B. CURING SAID MIXTURE OVERNIGHT; WHEREBY A NONREVERSIBLE GEL FORMS.

Unites States Patent 1 3,634,154

[72] Inventor George William Burdette [56] References Cited I N 532 2 Calii- UNITED STATES PATENTS [211 App o. Filed a 1963 3,492,177 1/1970 Rau et al 149/36X [45] Patented Jan. 11, 1972 Primary Examiner-Benjamin R. Padgett [73] Assignee The United States of America as y i scia and R. Miller represented by the Secretary of the Navy SOLID PROPELLANT COMPOSITION CONTAINING GELLED HYDRAZINE 8 Claims, No Drawings US. Cl 149/20, 149/36, 264/3 R Int. Cl. C06d 5/10, C [01 5/00, ClOl 7/00 Field of Search 149/36,

CLAIM: l. A method for the preparation ofa propellant composition which comprises the steps of a. stirring antimony] potassium tartrate crystals into a solution consisting of hydrazine and sodium carboxymethylcellulose at room temperature until a homogeneous mixture results, and b. curing said mixture overnight; whereby a nonreversible gel forms.

SOLID PROPELLANT COMPOSITION CONTAINING GELLED HYDRAZINE The invention described herein may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor.

The present invention relates to a propellant composition and to the preparation thereof; more specifically, to an improved high-performance solid propellant utilizing hydrazine in a system that is solid at ambient temperature.

Those concerned with the development of improved propellant systems have recognized the need for high-energy, highperformance solid propellants which have practical largescale production. The present invention fulfills this need.

It is an object of this invention to provide a composition for use as a solid fuel for hybrid rockets.

Another object is to provide a solid propellant composition with increased time for casting rocket motors (pot life).

A further object of the invention is the provision of a method for preparing a high-performance solid hybrid propellant which is economical, practical, and timesaving.

Other objects, features and many of the attendant advantages of this invention will become readily appreciated as the same become better understood by reference to the detailed description.

in order to utilize hydrazine in a high-performance propellant formulation that would be solid at ambient temperature additives are needed to effectively trap the relatively small hydrazine molecules. The approach taken was to form a polymeric gel utilizing hydrazine as the plasticizer. Many high molecular weight polymers were tested in an attempt to find some that were soluble in but not degraded by hydrazine. In table 1 below are listed some of the polymers that were tried at the percent level at room temperature.

TABLE 1. Polymers Tried for Hydrazine Gelation Of the various gelling agents tried sodium carboxymethylcellulose (CMC) looked most promising. However, this gel had little physical strength and the rate of gellation was too rapid resulting in shorter mixing and casting times than are desirable for large-scale processing. An effort to find a crosslinking agent for the hydrazine-sodium-carboxymethylcellulose system to strengthen the gel resulted in a series of experiments using various salts. Ferric hypophosphite and basic aluminum acetate favorably affected the gelling properties of aqueous carboxymethylcellulose (CMC) solutions. When these salts were tried in the hydrazine-sodium-carboxymethylcellulose solution, the results were unfavorable. Table 2 below is a tabulation of the various salts that were tried as cross-linking agents for the hydrazine-sodium-carboxymethylcellulose system at the 0.5 percent level.

Results Salts No additional strength No additional strength No additional strength Aluminum nitrate Aluminum sulfate Aluminum acetate No additional strength Gelled rapidly and was slightly stronger than unmodified gel Gelled slowly to form a weak gel Tough. rubbery gel Aluminum hydroxide Uranyl acetate Sodium potassium tartrate Antimonyl potassium tartrate An unmodified gel contains no salts.

It was apparent that antimonyl potassium tartrate which is quite soluble in hydrazine was by far the best cross-linking agent. Further investigation revealed that the most effective cross-linking occurs when an amount of antimonyl potassium tartrate equal to 15-20 percent by weight of the sodium carboxymethylcellulose in the system is used. Cross-linking begins upon addition of the antimonyl potassium tartrate to the sodium carboxymethylcellulose-hydrazine mixture and proceeds for several days. The cross-linked gels are much stronger than the uncross-linked gels making them more suitable for propellant application.

The invention is further illustrated by the following examples in which the percentages are by weight unless otherwise specified.

EXAMPLE 1 ingredients Weight i Antimonyl potassium tartrate (APT) l Hydrazinc (N,H,) Sodium carboxyrnethylcellulose (CMC) 9 The antimonyl potassium tartrate crystals were dissolved in the liquid hydrazine, then the sodium carboxymethylcellulose was stirred into the solution until a homogeneous mixture was obtained. In about 15 minutes the mixture thickened and on standing overnight a gray, tough nonreversible gel formed.

When the above ingredients were mixed thoroughly together the mixture remained very fluid for about 10 minutes at room temperature. On standing overnight a very tough nonreversible gel formed.

EXAMPLE 1]] Ingredients Weight-grams Antimonyl potassium tartrate 0.3 Hydrazine 9.0 Sodium carboxymethylcellulose 0.9

The above ingredients were thoroughly stirred until a homogeneous mixture resulted which remained fluid for about 10 minutes. Overnight it formed a tougher gel than the formulations set-forth in examples I and II above which used less antimonyl potassium tartrate. This gel was also very rubbery.

EXAMPLE IV Ingredients Weight 9i Uranyl acetate I Hydrazine 90 Sodium carboxymethylcellulose 9 The above ingredients were mixed together and a gel formed in about 5 minutes which on standing became quite tough.

EXAMPLE V Ingredients Weight $4 Antimony] sulfide I Hydrazine 90 Sodium carboxymethylcellulose 9 EXAMPLE VI Ingredients Weight-grams Antimonyl potassium lartrate Hydrazine Sodium carboxymethylcellulose The above ingredients were stirred together for about an hour until a homogeneous mixture resulted. Upon standing overnight the mixture cured to a flexible, nonflowing gel. After standing for one week the gel appeared unchanged and no hydrazine had condensed on the top. It was noted that the gel had turned a darker gray in color.

It was found that to increase the basicity of the system by adding amines such as unsymmetrical dimethylhydrazine (UDMI-I), tetramethylguanidine (TMG), and triaminoguanidine (TAG) effectively increased the pot life. In the following examples in which aluminum and zirconium powders were used as fuel additives, tetramethylguanidine was used primarily because of its effectiveness in small quantities and ease of handling.

The mixing technique for the hydrazine gel system containing the metal powder additives as above set out was fairly simple. The solid materials were blended thoroughly. and then the liquids, which had also been mixed, were added. The mixture 5 was stirred until homogeneity was obtained. Viscosity increases in the system as the sodium carboxymethylcellulose (CMC) gradually swells. After about 30 minutes the viscosity is sufficiently high to prevent settling of the aluminum particles. It was found that hydrazine prethickened with a small amount of sodium carboxymethylcellulose before being mixed with the other materials, causes a more rapid suspension of the metal additives before much swelling of the additional sodium carboxymethylcellulose (CMC) takes place. This rapid suspension method aids in producing a mix with a longer pot life. About 50 minutes is available for casting and other processing.

EXAMPLES VIII Ingredients Weight 71 Solid Components Aluminum Sodium carboxymethylcellulose Antimony! potassium tartrate Liquid Component Hydrazine TABLE 3.RESULTS OF PHYSICAL PROPERTIES TESTS ON CMC-HYDRAZINE-AI Elongation Maximum at maximum tensile tensile strength, strength, p.s.i. percent Curing time at room temperature y) Modulus, p.s.i./in./in.

Gel composition EXAMPLE IX Ingredients Weight Solid Components Zirconium 60. Aluminum 2.8 Sodium carboxymethylcellulose 6.9 Antimonyl potassium tartrate 1.? Liquid Components Hydrazine 28.5

Tetramethylguanidine (Ll The above ingredients were combined in the manner described in example VII. The mixture was cast in a small motor tube and stored at 60 C. for about 30 days. It built up a slight pressure and showed some slight decomposition after cooling to ambient temperature. This was thought to be caused by the reactivity of the zirconium powder due to its greater surface area resulting from its amorphous shape.

The antimonyl potassium tartrate was dissolved in the hydrazine, then the other solids which had been thoroughly mixed were added. The mixture set up in 5 minutes, and on standing overnight had gelled. Stretching tests showed it to be rubbery ant tough.

EXAMPLE XI Ingredients Weighb-grams Solid Components Zirconium (201.1.) I160 Sodium carboxymethylcellulose I23 Antimonyl potassium tartrate 32 Liquid Components Hydrazine Tetramethylguanidinc 1.5

In preparing this formulation the solid components were blended together and the liquid components were blended, then the solids were stirred into the liquid until homogeneity resulted. The mixture was cast into two propellant grains and cured for several days at ambient temperature. The zirconium was desensitized to electrostatic discharge by premixing it with the sodium carboxymethylcellulose binder before it is added to the hydrazine.

Metal powders such as beryllium, lithium, zirconium, aluminum and magnesium show considerable promise as fuel additives in solid propellant systems. Because of the high heat of combustion of these metals, it is postulated that their use in the hydrazine-gel propellant system will improve the specific impulse of the propellants.

Furthermore, the incorporation of wire screen structure into the gels will add additional physical strength. Several hydrazine-gel samples with screen reinforcement were prepared and proved to be superior in physical strength to unreinforced samples.

There is little, if any, new hazard involved in preparing the hydrazine containing propellant compositions. The necessary precaution associated with hydrazine work, such as avoidance of inhalation of hydrazine vapors and direct skin contact still hold. Hydrazine itself is considered insensitive to shock. No problem has been experienced with aluminum powder as small as 13;]. when added to hydrazine. The 201.1. zirconium powder is desensitized by premixing it with the powdered carboxymethylcellulose binder before it is added to the hydrazine.

When samples of gelled hydrazine containing aluminum or zirconium were attached to a mercury manometer at ambient temperature no gas evolution due to decomposition was observed.

r t l in Initial static firing tests of the metal-loaded hydrazine-gel system in a hybrid motor using chlorine trifluoride as the liquid oxidizer resulted in the ejection of unburned gel particles. The amount of unburned particles ejected during firing appeared to diminish considerably with the use of rigid gels that had been in storage for longer periods of time than those previously fired.

Obviously, many modifications and variations of the present invention are possible in the light of the above teachings. it is therefore to be understood that within the scope of the appended claims the invention may be practiced otherwise than as specifically described.

What is claimed is:

l. A method for the preparation of a propellant composition which comprises the steps of a. stirring antimonyl potassium tartrate crystals into a solution consisting of hydrazine and sodium carboxymethylcellulose at room temperature until a homogeneous mixture results, and

b. curing said mixture overnight; whereby a nonreversible gel forms.

2. A composition consisting of the following ingredients:

hydrazine sodium carboxymethylcellulose and antimonyl potassium tartrate.

3. A method for the manufacture ofa solid propellant grain comprising 1. preparing a mixture of up to percent by weight hydrazine, up to 12 percent by weight sodium carboxymethylcellulose and up to 4 percent by weight antimonyl potassium tartrate,

2. casting said mixture in a motor casing, and

3. curing for about 24 hours at ambient temperature,

whereby a nonreversible gel forms.

4. A composition consisting of the following constituents:

Antimony] potassium tartrate 5. A composition consisting essentially of the following constituents:

Solid Constituents Percent by weight Aluminum 46.3

Sodium carboxymethylcellulose 10.7

Antimonyl potassium tartrate 2.6 Liquid Constituent Hydrazine 40.4

6. A method for the preparation of solid propellant grains comprising a. preparing a dry mixture consisting essentially of aluminum powder, sodium carboxymethylcellulose and antimonyl potassium tartrate, b. stirring hydrazine into said mixture until a homogeneous composition results, c. casting the composition into a motor tube, and d. curing at a constant temperature of 60 C. for about 30 days. 7. A method for the preparation of solid propellant grains comprising a. preparing a dry mixture consisting of a metal powder selected from the group consisting of beryllium, lithium, zirconium, aluminum, and magnesium, or mixtures thereof, and a binder consisting of sodium carboxymethylcellulose; "b. preparing a liquid mixture consisting of antimonyl potassium tartrate crystals dissolved in hydrazine and c stirring said mixtures toge'the'r'until a viscous composition results,

I Y a d. castingthe composition intomotor tubes, and curing for 30 days at a temperature 'of about 60 C.

' 8'. ,Acompositionconsisting essentially of the following constituents Constituents i I W eig h'lgm ms Zirconium -2|0 Aluminum L Amimonyl potassium tartrqtc I 0,75,

Sodium carboxymeth'yiccflulose 2.25 I Hydrazine [0.0 

1. A METHOD FOR THE PREPARATION OF A PROPELLANT COMPOSITION WHICH COMPRISES THE STEPS OF A. STIRRING ANTIMONYL POTASSIUM TARTRATE CRYSTALS INTO A SOLUTION CONSISTING OF HYDRAZINE AND SODIUM CARBOXYMETHYLCELLULOSE AT ROOM TEMPERATURE UNTIL A HOMOGENEOUS MIXTURE RESULTS, AND B. CURING SAID MIXTURE OVERNIGHT; WHEREBY A NONREVERSIBLE GEL FORMS.
 2. A composition consisting of the following ingredients: hydrazine sodium carboxymethylcellulose and antimonyl potassium tartrate.
 2. casting said mixture in a motor casing, and
 3. curing for about 24 hours at ambient temperature, whereby a nonreversible gel forms.
 3. A method for the manufacture of a solid propellant grain comprising
 4. A composition consisting of the following constituents: Constituents Percent by weight Hydrazine 85 to 90 Sodium carboxymethylcellulose 9 to 12 Antimonyl potassium tartrate 1 to 4
 5. A composition consisting essentially of the following constituents: Solid Constituents Percent by weight Aluminum 46.3 Sodium carboxymethylcellulose 10.7 Antimonyl potassium tartrate 2.6 Liquid Constituent Hydrazine 40.4
 6. A method for the preparation of solid propellant grains comprising a. preparing a dry mixture consisting essentially of aluminum powder, sodium carboxymethylcellulose and antimonyl potassium tartrate, b. stirring hydrazine into said mixture until a homogeneous composition results, c. casting the composition into a motor tube, and d. curing at a constant temperature of 60* C. for about 30 days.
 7. A method for the preparation of solid propellant grains comprising a. preparing a dry mixture consisting of a metal powder selected from the group consisting of beryllium, lithium, zirconium, aluminum, and magnesium, or mixtures thereof, and a binder consisting of sodium carboxymethylcellulose; b. preparing a liquid mixture consisting of antimonyl potassium tartrate crystals dissolved in hydrazine and c. stirring said mixtures together until a viscous composition results, d. casting the composition into motor tubes, and curing for 30 days at a temperature of about 60* C.
 8. A composition consisting essentially of the following constituenTs Constituents Weight- grams Zirconium 21.0 Aluminum 1.0 Antimonyl potassium tartrate 0.75 Sodium carboxymethylcellulose 2.25 Hydrazine 10.0 